How do I find out the ratio of a rearend?
If you have your build sheet, look for a “G” option code and compare it to the option codes list–this will tell you what ratio is supposed to be in the car. John B (vegadad) has provided information about identifying a rear end here. To get a good guess, you can jack up the rear of the car (BOTH wheels). Mark one tire and mark the driveshaft. Turn the driveshaft until that tire makes one revolution. While you’re doing this, count the revolutions of the driveshaft. This number of revolutions is your ratio. Your ratio is not likely a whole number so you’ll have to estimate how much of a revolution the driveshaft makes as the tire finishes its rotation. The number of revolutions is the ratio. To be completely sure, open up the rear. Count the teeth on the pinion and on the ring gear. The number of ring teeth divided by the number of pinion teeth is the gear ratio. For example, a 1980 Monza 4cyl automatic has 41 teeth on the ring gear and 15 teeth on the pinion gear. 41/15 = 2.73333333, f
